This application claims the priority of Korean Patent Application No. 10-2005-0012425, filed on Feb. 15, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a method of manufacturing an optical device having a micromirror and, more particularly, to a method of manufacturing an optical device having a micromirror in which a micromirror widely used as an ultra-small optical component can be manufactured with high precision.
2. Description of the Related Art
Micromirrors are optical elements that have been widely used in optical pickup devices, optical communication systems and the like. Optical information storage devices having an optical pickup can record and reproduce information on and from an optical disc.
The optical information storage devices have been developed to reduce a wavelength of a light source and to increase a numerical aperture (NA) of an objective lens so that a high recording density can be achieved using optical energy. For example, optical information storage devices for CDs employ a light source having a wavelength of 780 nm and an objective lens having a numerical aperture (NA) of 0.45, and optical information storage devices for DVDs employ a light source having a wavelength of 650 nm and an objective lens having a NA of 0.6.
As users want to employ an optical disc in a portable information device, ultra-small optical pickups have been briskly developed. Optical pickups have been tried to be manufactured using semiconductor processes. In conventional optical pickup manufacturing processes, it takes a long time to adjust an optical axis between optical components when the optical components in units of several millimeters are assembled, and an automation rate is reduced. However, optical pickups can be manufactured at a wafer level using semiconductor processes so that mass-production is possible, small-sized optical pickups can be made and assembling and adjustment can be easily performed.
FIGS. 1A through 1E illustrate a conventional method of manufacturing a micromirror using semiconductor processes.
Referring to FIGS. 1A and 1B, a silicon ingot is cut to have a 9.74-degree off-axis angle with respect to a direction [011] of a plane (100) so as to form a silicon wafer 10 to a thickness of 500 μm. Referring to FIG. 1B, etching mask layers 11 and 12 are formed as SiO2 or SiNx on sides of the silicon wafer 10.
Referring to FIG. 1C, an etching window 13 is formed at a portion of the etching mask layer 11 using a photolithography process.
Referring to FIG. 1D, the silicon wafer 10 in which the etching window 13 is formed is soaked in a silicon anisotropic etching solution such as KOH or TMAH maintained at an appropriate temperature, thereby performing wet etching. When wet etching is performed for a predetermined amount of time, as shown in FIG. 1D, a first surface 15a having an inclined angle of about 45 degrees with respect to a lower surface of the silicon wafer 10 and a second surface 15b having an inclined angle of about 64.48 degrees with respect to the lower surface of the silicon wafer 10 are formed. Reference numeral 14 denotes an etched region of the silicon wafer 10.
Referring to FIG. 1E, the etching mask layers 11 and 12 are removed and the silicon wafer 10 is cut so that the first surface 15a and the second surface 15b are used as a micromirror.
The micromirror can be manufactured at a wafer level, and when a light source having a long wavelength is used or an etching depth is small, surface precision can be achieved. However, in the conventional method of manufacturing a micromirror shown in FIGS. 1A through 1E, when an etching depth is hundreds of μms, surface shaping precision cannot be easily substituted with shaping precision required in conventional optical components for optical pickups. For example, when the micromirror is used in the optical pickup, a micromirror array is manufactured and then is diced so that cracks occur in the micromirror array. When a process of bonding the micromirror array to a photodiode (PD) array is performed, the mirrormirror can be easily destroyed.
In the conventional method of manufacturing a large-sized micromirror having an array shape using an etching process, a large-sized Si wafer having high purity is used, experimental conditions should be strictly managed and a time required for etching a wafer is about 8 to 10 hours, which causes the cost of manufacturing the micromirror to increase.